Is the installbootloader step still needed? I vaguely remember something about when using UEFI it somehow was handled automatically (omnios.org/info/migrate_rpool)

not just UEFI, on attach event (that is, zpool attach does generate attach sysevent), the actions from /etc/sysevent/config/SUNW,EC_zfs,ESC_ZFS_bootfs_vdev_attach,sysevent.conf are run. Also, when you do beadm activate, then libbe will update boot programs if needed.

Ooh nice!

Will be replacing a dead nvme to

Morrow

And vaguely remembered something like that, but all docs pointed to having to do it manually